This invention relates generally to a filmstrip metering device adapted to lock a filmstrip after one frame thereof has been wound due to the operation of a wind-up member, and more particularly to such a device for metering a filmstrip having each frame thereof provided with a single metering perforation with a sensing member being engageable with a filmstrip metering perforation, the wind-up member being provided on a side of a camera body.
With a camera of this type, the winding of one frame of a filmstrip and the cocking of the shutter are both effected by operating the filmstrip wind-up member. When one frame of a filmstrip has just been wound, the filmstrip has to be locked so as to interrupt its winding around a shaft.
Filmstrip metering devices for use in a camera of this type are classified into three categories:
(1) When a filmstrip has been wound a given length, the movement of a wind-up member or the movement of a member associated therewith is forcibly interrupted. (See U.S. Pat. No. 3,820,142)
(2) When a filmstrip has been wound a given length, a transmission mechanism then disposed between a filmstrip winding shaft and a filmstrip wind-up member is interrupted. (See U.S. Pat. No. 3,829,975)
(3) A clutch mechanism is disposed between a filmstrip wind-up member and a transmission member adapted to transmit the movement of the filmstrip wind-up member to a filmstrip winding shaft, while a meshing engagement between the filmstrip wind-up member and the transmission member is released by means of the clutch mechanism, when a given length of a filmstrip is wound.
However, the approach according to category (1) requires that a cocking operation of the shutter be completed simultaneously with the completion of winding one frame of the filmstrip by the operation of the filmstrip wind-up member, with the result that the length of a filmstrip to be fed until the completion of cocking of the shutter is progressively increased, depending on the length of the filmstrip wound about a filmstrip winding shaft, thus providing varying spacings between each two frames of a filmstrip.
The approach according to category (2) requires the use of planetary gears of a complicated construction in a transmission member. This leads to a complicated construction of a filmstrip metering device, and hence highly accurate members or parts must be provided, with a resulting increase in cost.
The category (3) approach uses a clutch mechanism, such that when gears of a transmission member mesh with gears of a film wind-up member by means of the clutch mechanism, a high winding load is directly applied to transmission gears, with the resulting incomplete meshing between gears. As a result, a filmstrip is wound, with edges of teeth of one gear being urged against edges of teeth of another gear.